1. Field of the Invention
The present invention relates to a process for producing a curable resin and a curable coating composition containing said resin, and more particularly to a process for producing a novel curable resin capable of being cured by the exposure to radiation or heat and a curable coating composition containing said resin.
2. Prior Art
Recently, a so-called curable resin which reacts to form linked cross structures by the exposure to radiation or heat has been frequently used as an important component for solvent-free compositions in the technical field of coating compositions including paints and inks and also in the technical field of adhesives.
For example, the demand for the improvement of printing speed has been increasing along with the development of the printing technology. With the increase in the demand for higher printing speed, the serious demand for the improved drying speed (curing speed) of printing inks has been more and more growing. In the conventional high speed printing, the printed products are dried by direct-heating system or by hot-air system as the means for promoting the drying of the printed products. From 30 to 40% of the solvent contained in the printing inks which are used in such heat-set printing as mentioned above is evaporated by heating to dry the inks. Therefore, a part of the solvent vapor produced in the printing factories causes pollution problems more often than ever.
Therefore, printing inks, of such a type as can be dried by some means or other without the need for discharging such volatile material as mentioned above, have been desired by those skilled in the art.
Under these circumstances, there are demands for printing inks which can be dried without being accompanied by the evaporation of solvent, such as ultraviolet ray curing inks or thermosetting type nonsolvent inks. In fact, there have already been made proposals for such printing inks.
For example, in Kokai Pat. Publication No. 124133/74 (Unexamined Patent Application Publication No. 124133/74), it is disclosed that excellent mutual solubility and curing property can be attained when a resin obtained by esterifying copolymer resin of dicyclopentadiene and allyl alcohol with (meth-)acrylic acid, is used as curable ink.
However, when the resin disclosed in the above cited Kokai Patent Gazette is used as the curable coating composition, drying speed is not sufficient and, the exposure sensitivity thereof is poor; thus, the printing inks of this type do not meet the original requirement of the printing inks for high speed printing.